1. Field of Invention
The field of the present invention relates in general to modems and more particularly reducing power dissipation across multiple transmission systems.
2. Description of the Related Art
North American Integrated Service Digital Network (ISDN) Standard, defined by the American National Standard Institute (ANSI), regulates the protocol of information transmissions over telephone lines In particular, the ISDN standard regulates the rate at which information can be transmitted and in what format. ISDN allows full duplex digital transmission of two 64 kilo bit per second data channels. These data rates may easily be achieved over the trunk lines, which connect the telephone cornpanies"" central offices. The problem lies in passing these signals across the subscriber line between the central office and the business or residential user. These lines were originally constructed to handle voice traffic in the narrow band between 300 Hz to 3000 Hz at bandwidths equivalent to several kilo baud.
Digital Subscriber Lines (DSL) technology and improvements thereon including: G.Lite, ADSL, VDSL, HDSL all of which are broadly identified as X-DSL have been developed to increase the effective bandwidth of existing subscriber line connections, without requiring the installation of new fiber optic cable. An X-DSL modem operates at frequencies higher than the voice band frequencies, thus an X-DSL modem may operate simultaneously with a voice band modem or a telephone conversation. Currently there are over ten discrete X-DSL standards, including. G.Lite, ADSL, VDSL, SDSL, MDSL, RADSL, HDSL, etc.
One of the primary factors limiting the bandwidth or channel capacity of any of the above discussed X-DSL protocols is power. Large amounts of power are required to drive high baud rates across subscriber lines or other wired or wireless communication media Most of the power in X-DSL systems is consumed in the line driver which drives the modulated signal onto the subscriber line. The line driver may account for 60% or more of the overall system power requirement.
Typically the modulated signal supplied to a line driver has a normal power distribution, meaning that the peak-to-average power ratio is relatively high. Thus to avoid clipping or other distortion the occasional high peak signals require a high voltage supply. Recently efforts have been made reduce the amount of power consumed in a line driver by use of multiple power levels. Texas Instruments THS6032 Class G amplifier architectures uses four power supplies at +/xe2x88x925 and +/xe2x88x9215 Volts to reduce power consumption. The ADSL line to which this amplifier is coupled is driven at higher voltage levels only when required. U.S. Pat. No. #6,028,486 entitled xe2x80x9cMethod and Apparatus for Reducing Power Dissipation in Multi-Carrier Amplifiersxe2x80x9d issued on Feb. 22, 2000 and assigned to Telefonaktiebolaget L M Ericsson also teaches apparatus for reducing power in a DSL line driver. In a first embodiment, resembling that employed in the Texas Instruments device, a single amplifier is switchably connected to high and low power supplies, in response to the threshold level of an input signal. In a second embodiment dual amplifiers one with a high power supply and the other with a low power supply are switchably connected to the load in response to the threshold level of an input signal. Both the Texas Instruments and Ericsson designs require an increase in the number of power supplies and/or amplifiers associated with a subscriber line.
What is needed are approaches to power reduction with an improved form factor when compared with the prior art designs.
An apparatus and method for reducing power requirements in X-DSL and other communication protocols is disclosed. The apparatus may be applied with equal advantage in wired and wireless media Power is supplied selectively to input lines in which input signals exceed selected threshold levels. The apparatus is configured to support statistical multiplexing of the input signal lines across a plurality of amplification means which support amplification at up to either of at least two power levels. This reduces overall power requirements for the combined input lines.
In an embodiment of the invention an apparatus for providing amplification of input signals on corresponding ones of a plurality of input signal lines is disclosed. The apparatus includes: primary amplifiers, at least one secondary amplifier, a selector and switches. The primary amplifiers each include an input and an output, with each input coupled to a corresponding one of the plurality of input signal lines. Each of the plurality of primary amplifiers are capable of receiving a corresponding input signal and generating an output signal at up to a first power level. The at least one secondary amplifier also includes an input and an output. The at least one secondary amplifier is responsive to a selected input signal at the input to generate at the output an output signal at up to a second power level greater than the first power level. The selector includes inputs coupled to each of the input signal lines to select at least one input signal line with an input signal amplitude above a selected threshold for amplification by the at least one secondary amplifier. The switches are responsive to the selector for switchably coupling the at least one secondary amplifier to the at least one selected input signal line.
In an alternate embodiment of the invention the apparatus for providing amplification of amplification of input signals includes amplifiers, a first power supply, at least a second power supply, a selector and switches. The plurality of amplifiers each include a signal input, a signal output, and a power supply input. Each signal input is coupled to a corresponding one of the plurality of input signal lines. Each of the plurality of amplifiers is capable of receiving a corresponding input signal and generating an output signal. The first power supply generates a corresponding first power level. The at least a second power supply generates at least a corresponding second power level greater than the first power level. The selector inputs are coupled to each of the input signal lines to select at least one input signal line with an input signal amplitude above a selected threshold; for amplification at up to the second power level. The switches are responsive to said selector for switchably coupling said at least a second power supply to the power supply input of the corresponding at least one of the plurality of amplifiers coupled to the at least one selected input signal line and further switchably coupling power supply inputs of remaining unselected ones of the plurality of amplifiers to said first power supply.
In an another embodiment of the invention a method for amplifying of input signals on corresponding ones of a plurality of input signal lines is disclosed. The method comprises the acts of:
detecting which among the input signal lines includes input signal amplitudes above a selected threshold;
choosing among the input signal lines with input signal amplitudes above the selected threshold, at least a selected one of the input signal lines for further amplification;
amplifying the at least a selected one of the input signal lines at up to at least a second power level greater than a first power level, and amplifying remaining unselected ones of the input signal lines at up to the first power level.